1. Field of the Invention
The present invention relates to a photochromic compound, a photochromic composition, and a photochromic functional element using the same. More particularly, the present invention relates to a photochromic functional element which can be used in an anti-glare mirror for automobile or such.
2. Description of the Related Arts
In the conventional automobile mirror, a technique has been developed which imparts mirror to an anti-glare property in order to improve visibility. The term “anti-glare property” used herein is a property that sunshine in the daytime, a headlight of next car in the nighttime and the like are reflected by an automobile mirror to decrease dazzling felt by a driver or a fellow passenger. As a mirror possessing such an anti-glare property, there is a mirror which utilizes a color mirror (so-called blue mirror) having a reflectance peak at a blue side (short wavelength side) and having a blue color on the surface thereof.
The human visibility has a peak at a wavelength of approximately 555 nm under a light condition, and yellowish green color becomes clearly visible. As the surroundings become dark, the peak of the visibility is gradually shifted toward a blue side, and the peak wavelength is to be at approximately 505 nm. In the blue mirror, the peak of reflectance characteristic exists in a range of from 400 to 510 nm. Consequently, the image reflected by the blue mirror has a peak deviating from the peak of the human visibility in the daytime and, thus it looks slightly dark, preventing dazzling of the sunshine. In the nighttime, the blue mirror has a peak accorded with the peak of the human visibility and, thus, the reflected image looks bright, excelling in visibility.
Typical examples of the conventional techniques which impart anti-glare property to an automobile mirror include those which apply a liquid crystal material, electrochromic material or such. Amongst them, a reflectance-variable, automobile mirror utilizing an electrochromic material will be described (See Japanese Patent Laid-Open No. 09-120,088).
As shown in FIG. 8, in an automobile mirror 300 having a reversibly variable transmittance, a prism-shaped mirror 180 is laminated on a surface 131 of a device having a reversibly variable transmittance by means of a transparent laminating material (layer 19). The prism-shaped mirror 180 comprises a prism-shaped piece 18 composed of an essentially transparent solid material (such as glass or transparent plastic), and a layer 18A of a highly reflective material (such as silver) adhered onto the surface of the solid material by a technique common to the mirror processing field, so that a light passing through the solid material and arriving at the reflective material layer is reflected toward the original direction via the solid material layer in a high ratio (preferably at least approximately 80%). The highly reflective layer 18A makes up reflective means for mirror.
The mirror comprises devices (electrochromic devices) having a reversibly variable transmittance through which a light before and after reflected from the reflecting means is passed. A wall 100, electrochromic elements 10 and 10A; a wall 130, electrochromic elements 13 and 13A; a spacer 11; a solution space 12; and a line or a strip 16 shown in FIG. 8 correspond to elements for the device (not shown), and the line or strip shown in FIG. 8 extends to lead lines of the device (not shown). The lead lines of the device (not shown) are connected to an element for controlling power supply (for example, switching means, means for controlling electric potential between electrodes).
The automobile mirror having a reversibly variable transmittance configured as described above is usually in a bleached state, where a light entering from the wall 100 (which is a solid material comprising glass or transparent plastic) is passed through the interiors of the electrochromic elements 13 and 13A, and is reflected at the reflective means 18A to be in a highly reflective state, exhibiting a function as a mirror. At the time of coloration, the light transmittance thereof is decreased so that the device is to be in a low reflective state where the reflected light is decreased, exhibiting an anti-glare function. In the case where such electrochromic elements are utilized in antiglare mirror, responding to the application of voltage and to making a short circuit, mutual switching between the coloration at the time of exhibiting anti-glare function and the bleaching at a usual mode is carried out.
However, in the automobile mirror having a reversibly variable transmittance utilizing such electrochromic elements, a sensor, which can be sensitized by a relatively strong light such as sunshine and a light from a head light of next car, a control circuit which controls the actuation of the electrochromic elements based on a signal produced from the sensor and other device should be separately required, leading to a problem associated with complicated configuration.
So, glazing has been suggested in Japanese Patent Laid-Open No. 10-114007 in which a photochromic material, whose absorbance at a visible light region is reversibly varied upon irradiation of a light with a specific wavelength is applied to glazing so that the glazing can become dark upon receiving a strong light such as sunshine whereby the light reflectance thereof is decreased to prevent a driver and others who get into a car from being dazzled (Japanese Patent Laid-Open Publication No. 10-114007).
Examples of the photochromic materials applied to this glazing include a material comprising a silver salt, particularly a silver halide, as an active component dispersed in a glassy matrix so that the active component such as the silver halide just mentioned is reversibly transformed into a state of a metal bonded body, and a material comprising an organic dyestuff (pigment) as an active component dispersed in a polymeric matrix.
In the glazing utilizing the latter material, the photochromic material absorbs a light in an ultraviolet region to thereby be reversibly isomerized, causing coloration or bleaching in a reversible manner. Typical examples of the organic pigments include compounds derived from spirooxazine and spiropyran.
However, in the glazing utilizing the photochromic material described above, irradiation of ultraviolet light contained in sunshine is required for causing coloration and bleaching of the photochromic material in a reversible manner. For this reason, even if a light from a head light of an oncoming car enters into the glazing, it has been difficult to color the mirror enough for preventing a driver or such from dazing due to its weak strength of ultraviolet light in the automobile head light. Consequently, in such a case, a light source, which can irradiate the photochromic materials with an ultraviolet light at a strength sufficient for reversibly changing coloration and bleaching, is required to be separately placed. This poses a problem in terms of insufficient practical use.
The present invention has been made in light of the above problems, and a first object of the present invention is to provide a photochromic material, which does not exhibit any photochromic property in response to a light having a wavelength within a visible region and which is sensitized by a light having a given wavelength within a wavelength region of not less than 700 nm (particularly infrared region) and absorbs a light in visible region, and to provide a functional element using such a phenomenon. Specifically, in the photochromic material and the photochromic phenomenon according to the present invention, since it is sensitized by a light having a specific wavelength within a wavelength region of not less than 700 nm (particularly infrared region) to exhibit a photochromic property, a light having a wavelength in ultraviolet region is not required for the photochromic property.
A second object of the present invention is to provide a functional element such as a photochromic display element applicable to an automobile mirror having an anti-glare property utilizing such a photochromic material and such a photochromic phenomenon as described above.